1. Technical Field
The present invention relates to a wireless communication system, and more particularly, to a method for transmitting channel information in a wireless communication system.
2. Related Art
The institute of electrical and electronics engineers (IEEE) 802.16 standard provides a technique and protocol for supporting broadband wireless access. The standardization had been conducted since 1999 until the IEEE 802.16-2001 was approved in 2001. The IEEE 802.16-2001 is based on a physical layer of a single carrier (SC) called ‘WirelessMAN-SC’. The IEEE 802.16a standard was approved in 2003. In the IEEE 802.16a standard, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ are further added to the physical layer in addition to the ‘WirelessMAN-SC’. After completion of the IEEE 802.16a standard, the revised IEEE 802.16-2004 standard was approved in 2004. To correct bugs and errors of the IEEE 802.16-2004 standard, the IEEE 802.16-2004/Cor1 was completed in 2005 in a format of ‘corrigendum’.
A mobile station (MS) transmits, to a base station (BS), channel information required by the BS to schedule downlink radio resources. The channel information may be an adaptive modulation and coding (AMC) band bitmap, a channel quality indicator (CQI), rank information (RI), a precoding matrix indicator (PMI), etc. The BS schedules the radio resources by using the channel information received from the MS.
FIG. 1 is a flow diagram showing an example of a method for transmitting channel information according to the conventional IEEE 802.16 standard.
Referring to FIG. 1, an MS transmits a permutation type change request to a BS (step S100). For example, an MS may request permutation type to be changed from a normal permutation type to an AMC type. Examples of the normal permutation type include full usage of subchannels (FUSC) and partial usage of subchannels (PUSC) using an open loop mode, and AMC type using a closed loop mode. Upon receiving the permutation type change request, the BS transmits a report-request message for channel measurement to the MS (step S110). In response to the report-request message, the MS transmits a report-response message to the BS (step S120). The report-response message includes an AMC band bitmap. Further, the MS periodically transmits channel information (e.g. CQI, PMI, etc.) to the BS (step S130). The BS schedules downlink radio resources by using the received CQI, PMI, etc. (step S140).
In this case, the MS transmits information for the AMC band bitmap to the BS only when the report-request message is received from the BS. Since the information for the AMC band bitmap is non-periodically transmitted, there is a problem in that, when the information for the AMC band bitmap is changed in the middle of transmission, the changes in the information cannot be flexibility handled. In addition, the report-response message is unreliable as a medium access control (MAC) message, which may result in an error in a process of transmitting the message. Therefore, there is a need for a new method for reliably transmitting important information such as the AMC band bitmap.